The present invention relates to ATM transmission, and more particularly to a bandwidth control method in the ATM transmission that can fulfill required service qualities in the transmission.
Generally, an ATM transmission system multiplexes cells with different quality conditions such as delay and a cell loss ratio, and transmits them through an output transmission path. To achieve such transmission, it is necessary for each quality class to have a plurality of buffers at a stage previous to the multiplexing.
The ATM transmission system also multiplexes packets with different quality conditions into ATM cells to be transmitted. To achieve such transmission, it is also necessary for each quality class to have a plurality of buffers at a stage previous to the multiplexing into the ATM cells.
Besides, there is an ATM transmission technique that multiplexes packets from a plurality of users into ATM cells to be transmitted. ATM adaptation layer type 2 (AAL type 2) can multiplex a maximum of 248 users into a single virtual channel (VC) connection to be transmitted. Since the quality class is usually required for each user connection, a plurality of quality classes must be prepared in the VC connection so that the transmission is carried out with the quality that meets the requirement of each user connection.
A system configuration for multiplexing packets consisting of a plurality of connections into ATM cells is disclosed, for example, in xe2x80x9cMultiplex Transmitter for Micro-framexe2x80x9d, an international application filed by the assignee of the present application (International Publication No. WO97/23975 published Jul. 3, 1997). Its disclosure has a plurality of buffers for each quality class, distributes to the buffers packets input to the multiplex transmitter, and extracts the packets from the buffers in predetermined order, thereby achieving transmission according to the quality classes.
In this case, the bandwidth to be assigned to each quality class is decided from the rate of extracting the cells or packets from the buffers of each quality class, to which they are delivered. However, establishment of a requested user connection sometimes becomes impossible because of the limited bandwidth set for each quality class, even if the total bandwidth of the transmission path has some leeway.
As described above, a system configuration is already present which enables the transmission of different qualities by loading a plurality of buffers with packets with different quality conditions such as delay and cell loss ratios, and by multiplexing them into ATM cells, in which the bandwidth of the transmission path is allotted to respective quality classes.
Generally, bandwidth ratios of respective quality classes are determined from traffic qualities estimated at the start of the multiplex system, and the packets or cells are extracted at the rates that meet the determined bandwidth ratios. However, estimating actual traffic qualities is not easy, and hence it is not unlikely that the bandwidth required for transmission can exceed the bandwidth assigned to the current quality class even if there is some bandwidth margin in the transmission path in its entirety. Thus, the connection establishment request is rejected because of the limited assigned bandwidth which cannot satisfy the service quality needed for the transmission. However, if the established bandwidth ratios can be changed, the transmission that fulfills the service quality can be achieved, enabling more connections to be accepted with maintaining small delay and cell loss ratios.
It is therefore an object of the present invention is to implement efficient use of a transmission path in response to irregular traffic qualities of various types of services with different quality conditions in an actual environment by providing a multiplex system, which outputs multiplexed information to a transmission path, with bandwidth change control.
To accomplish the foregoing object, the present invention provides a multiplex transmission system for carrying out multiplex transmission of ATM cells, the multiplex transmission system comprising: separate buffers, each allotted to one of quality classes, wherein accepting separately in the buffers transmission contents from a plurality of connections; changing extraction rates from the buffers; and changing allotments of bandwidths to be assigned to channels of respective quality classes by changing the extraction rates.
The transmission contents from a plurality of connections can consist of ATM cells or packets In the case of packets, they are extracted from the buffers, and multiplexed into ATM cells to be output. The system can be configured as a combination of them.
Allotments of bandwidths assigned to channels associated with respective quality classes can be changed when a request is made for establishing a new connection.
In addition, the allotments of bandwidths assigned to channels associated with respective quality classes can be changed when a request is made for releasing a currently communicating connection.
The allotments of bandwidths assigned to channels associated with respective quality classes can be changed when a request is made for establishing a new connection, and a bandwidth which is required for a quality class associated with the new connection after adding the new connection exceeds a bandwidth which has been assigned to the quality class associated with the new connection.
Furthermore, the allotments of bandwidths assigned to channels associated with respective quality classes can be changed when any one of cell loss ratios which are monitored for respective quality classes exceed a predetermined value.
The multiplex system with the foregoing configurations can implement the effective use of the transmission path.